Division of Cryptogamic Botany and Plant 



Pathology. 



I submit herewith the report of the division of cryptogamic 

 botany and plant pathology of the Cornell University Agri- 

 cultural Experiment Station for the year 1894. 



Since the last annual report an extended bulletin (No. 73) was 

 prepared and published on " Leaf Curl and Plum Pockets." 

 These are deformities of the leaves, twigs and fruits of the genus 

 prunus (plum, peach, cherry, etc.) produced by the parasitism of 

 certain fungi belonging to the Exoascaceae. The investigation 

 quite unexpectedly brought to light several undescribed species 

 and several European ones not heretofore known to exist in the 

 United States. So far as known the species are strictly obligate 

 parasites and present the peculiarity, especially in the species 

 possessing a perennial mycelium, of resisting, to a certain extent, 

 attempts to inoculate unaffected trees artificially by the sowing 

 of the spores or by transplanting portions of the deformed tissue. 

 So far as experience goes, it appears a difficult thing to do in 

 such species. In these the mycelium lives dormant in the buds 

 and affected trees during the winter ready to produce- the char- 

 acteristic deformities again the following spring. In some of 

 these cases it is quite certain that the disease is transferred from 

 affected stock to young or healthy trees by the process of 

 budding. By proper precaution in selecting trees entirely free 

 from the disease this common source of infection may be avoided. 

 This close or inbred obligate parasitism of these species is prob- 

 ably one reason for the evolution of so large a number of species 

 found upon the different species of ^Prunus. 



